This invention relates to a cathodic electrodeposition paint composition. More particularly, it relates to a cathodic electrodeposition paint useful in one or two coats finish of steel substrates.
Electrically deposited paint films may be susceptible to a variety of appearance defects upon curing for a number of reasons. One of such defects is tiny craters induced by oil droplets or other particulate matter deposited throughout the wet films. It is known that such cratering may be prevented or minimized effectively by increasing the viscosity of the surface layer of wet paint films and a variety of additives useful for this purpose have been proposed.
Apart from the cratering, the paint films may be susceptible to another appearance defect hereinafter referred to as "stripe-like recess" for a totally different reason. The stripe-like recesses appear locally on the cured paint films as waves of stripe-like surface irregularities. It is postulated that the cause of stripe-like recesses is present in the metallic substrate onto which the paint is applied. Prior to applying the paint electrically, the substrate is usually subjected to certain pretreatment steps including degreasing and phosphate treatment. When the substrate is not thoroughly degreased or not thoroughly rinsed after degreasing, any residues tend to be concentrated in a localized area upon drying to form wave-like patterns of deposited matter. These patterns are not visible with naked eyes and subsequently develop into visible patterns only after the substrate is finished with an electrodeposition paint.
Because the cause of its occurrence is different, it is apparent that known methods for the prevention of cratering would not be effective for the prevention of stripe-like recesses.
It is, therefore, a principal object of the present invention to provide a cathodic electrodeposition paint composition, particularly for use in one or two coats finish which is hardly susceptible to stripe-like recesses.